As the efficacy (measured in lumen per Watt) and the luminous flux (measured in lumen) of light emitting diodes (LEDs) continues to increase and prices continue to go down, LED illumination and LED-based luminaires are becoming viable alternatives to and at a competitive level with until now predominant common light bulbs or tube luminescent based lamps for providing large-area illumination.
By using LEDs it is possible to decrease the energy consumption, a requirement which is well in line with the current environmental trend. Further, as a consequence of having the possibilities to provide bright light even when using compact LEDs, a number of lighting systems has been proposed greatly differing from the standard lighting systems comprising a common light bulb. In line with this and by means of using LEDs instead of light bulbs, a user is also given a more flexible control of the lighting system illumination functionalities, for example in relation to intensity dimming control or beam direction.
An example of such a lighting system is disclosed in WO 2011/039690, describing a modular luminaire 100 comprising two light-emitting portions 102 and 104, as shown in FIG. 1. The two portions are individually controllable and are configured to provide complementary beam patterns. The portion 102 includes light sources 106 and is adapted to generate a relatively narrow beam of light illuminating a narrow, task, area. The portion 104 includes light sources 108 and is adapted to generate a relatively wide, batwing-type beam of light providing ambient illumination of a background area surrounding the task area. Besides providing the advantages of a lower cost and a higher comfort level in comparison with conventional office luminaires, such a split beam luminaire enables a local dimming lighting solution with higher energy savings because it allows selectively dimming of lighting fixtures that are not directly above occupied task areas. However, even with such an advanced luminaire, it is always desirable to try to reduce energy consumption even further.